Brake booster question...
Thread Starter
Melting Slicks
Joined: Jan 2005
Posts: 3,347
Likes: 9
From: Salinas Ca.
Brake booster question...
I have new MC, booster, new stainless lines (complete) new calipers, and new rubber lines to all wheels. Im having trouble bleeding. What I've done, bench bleed the MC.. took a mightvac and pulled Dot 5 to all calipers, still getting air after the second go around. I attempt to pump brake peddle so I can bleed at the wheels, no go... When I pump (peddle) I have very little pump stroke ( where I feel resistance) which is at the very bottom of the peddle. Like the last inch!!! After re-bench bleeding the MC two more times, I look inside the Booster and push back the diaphram with the end of a socket wrench. It seems to me that the diaphram should be pushed back with the MC plunger (so as to get some stroke). When I push the diaphram back by hand and reinstall the MC the peddle get one good stroke and then acts the same as above. Please advise...this is driving me crazy. Thanks Don
Racer
Joined: Feb 2006
Posts: 295
Likes: 0
From: Bristol VA
I installed new master cyl & booster in my 75 had same problem after changing out everything lines, proportioning valve etc. I still had air in the lines after a lot of bleeding ( 3quarts dot 5 ) no change! I bought a pressure bleeder and that worked somewhat I had good pedal but was a little spongy. The car stopped but I did not like the feeling after a long talk with a local Corvette shop he said get rid of the dot 5 flush all the lines and put in dot 3. I did what he said and WOW the car stops great. Hope this helps.
Former Vendor
Joined: Nov 2005
Posts: 683
Likes: 1
From: Mounds View Minnesota
Muddy
It kinda sounds like your booster is bad.
Here's what I'd check.
Look in the MC as the pedal is slowly pressed, you should see the piston go by the small holes in the bottom of the resivour.
Then when the pedal is allowed to return you should be able to see the piston retract.
Another thing to check is if the pedal push rod is coming free of the booster.
Fist reach up and wiggle the brake pedal push rod. it should not flop around much at all if any.
Next make sure the brake pedal is all the way up and against the stops.
Next Press the brake pedal with your hand and see if you can feel a sudden contact between the booster and the push rod.
Any of the above would point to the booster or the brake pedal hanging up and not retracting fully.
If thats not the problem then I'm clueless.
Keith
It kinda sounds like your booster is bad.
Here's what I'd check.
Look in the MC as the pedal is slowly pressed, you should see the piston go by the small holes in the bottom of the resivour.
Then when the pedal is allowed to return you should be able to see the piston retract.
Another thing to check is if the pedal push rod is coming free of the booster.
Fist reach up and wiggle the brake pedal push rod. it should not flop around much at all if any.
Next make sure the brake pedal is all the way up and against the stops.
Next Press the brake pedal with your hand and see if you can feel a sudden contact between the booster and the push rod.
Any of the above would point to the booster or the brake pedal hanging up and not retracting fully.
If thats not the problem then I'm clueless.
Keith
Thread Starter
Melting Slicks
Joined: Jan 2005
Posts: 3,347
Likes: 9
From: Salinas Ca.
Ricky2525...thanks for the input and yes... I am getting a little tight with the Dot 5!!! ummmm.
Keith, thanks heaps for the phone conversation, needless to say, sure wish I was in your neighborhood, smile. Hey, if you have anymore questions regarding your tile... don't hesitate in contacting me
Again thanks! Don
Keith, thanks heaps for the phone conversation, needless to say, sure wish I was in your neighborhood, smile. Hey, if you have anymore questions regarding your tile... don't hesitate in contacting me
Again thanks! Don
Intermediate
Joined: Jun 2004
Posts: 41
Likes: 0
From: Hamilton Ontario
Brake bleeding
Hi Muddy
Try bleeding again with the motor idling and a more normal brake feel will be there. A little spongy though, until the air is bled out.
I notice the kind of feel you reported when I pump the brake while the car is in cold storage up here in Canada. Aah, a few more months till spring.
Try bleeding again with the motor idling and a more normal brake feel will be there. A little spongy though, until the air is bled out.
I notice the kind of feel you reported when I pump the brake while the car is in cold storage up here in Canada. Aah, a few more months till spring.
Thread Starter
Melting Slicks
Joined: Jan 2005
Posts: 3,347
Likes: 9
From: Salinas Ca.
Keith (Corvette Engineering) hit it right on the head. Keith through this forum supplied me with his phone number. I called him and he troubled shooted my problem long distance with me standing beside my baby. His conclusion, was the booster. This boster is brand new which I purchase last spring just before the restore. I can't believe it. I suppose thats what you ge for a rebuild, ummm. Anyway, got a stiff peddle now and plenty of grins on behalf of Keith! Your the man Keith. After the brakes, I loaded up the LT-1 on a trailer where we'll get a complete stainless exhaust tomorrow. Yeepeeee! 
On that note: I thank everyone in concern and will post pic's of the new exhaust. Cheers Don
On that note: I thank everyone in concern and will post pic's of the new exhaust. Cheers Don
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